This invention relates generally to semiconductor lasers and more particularly to such lasers having a modified active region and/or adjacent cladding regions to provide for lower thermal resistance, improved optical confinement, improved optical confinement, lower series resistance and beam width control.
Over the past several years, there have been improvements made in the threshold current density of single and multiple quantum well (SQW & MQW) heterostructure semiconductor lasers as well as an increase in T.sub.0, which has been a traditional indicator of threshold/temperature dependence in laser operation. High values of T.sub.0 correspond to low sensitivity of laser current threshold to operating temperature. These improvements have been made in such quantum well lasers by first providing separate confinement heterostructure quantum well laser (SCH QW) structures having a single quantum well (SQW) or multiple quantum well (MQW) active region (See, for example, the article of Thompson et al "(GaAl)As Lasers With a Heterostructure for Optical Confinement and Additional heterojunctions for Extreme Carrier Confinement", IEEE Journal Of Quantum Electronics, Vol. QE-9, pp. 311-3, (1973) and USPs 4,328,469 and 4,602,370), followed by graded index (SCH SQW or MQW separate confinement heterostructures quantum well lasers (GRIN SCH QW) having a (1) parabolic graded function or (2) linearly graded function or (3) stair step graded function or (4) barrier thickness graded function in the cladding layers adjacent to the active region. Examples of these four types of graded index cladding region profiles are respectively found in:
(1) U.S. Pat. Nos. 4,512,022 Tsang and 4,630,083 to Yamakoshi; T. Hayakawa et al, "Low Current Threshold AlGaAs Visible Laser Diodes With An (AlGaAs).sub.m (GaAs).sub.n Superlattice Quantum Well", Applied Physics Letters, Vol. 49(11), pp. 636-638, Sept. 15, 1986; and P. L. Derry et al, "Ultralow-Threshold Graded-Index Separate-Confinement Single Quantum Well Buried Heterostructure (Al,Ga)As Lasers With High Reflectivity Coatings", Applied Physics Letters, Vol. 50(25), pp. 1773-1775, Jun. 22, 1987. PA1 (2) S. D. Hersee et al, "Very Low Threshold GRIN-SCH GaAs/GaAlAs Laser Structure Grown By OM VPE", Electronics Letters, Vol. 18(20), pp. 870-871, Sept. 30, 1982. PA1 (3) S. D. Hersee et al, "Low-Threshold GRIN-SCH GaAs/GaAlAs Laser Structure Grown By OM VPE", Electronics Letters, Vol. 18(14), pp. 618-620, Jul. 8, 1982. PA1 (4) J. R. Shealy, "Optimizing the Performance of AlGaAs Graded Index Separate Confining Heterostructure Quantum Well Lasers, Applied Physics Letters, Vol. 50(23), pp. 1634-1636, Jun. 8, 1987.
It is a principal object of this invention to provide improved current density threshold structures independent of waveguide parameters with a better degree of beam width control, improved higher thermal conductivity and lower sensitivity to temperature with attendant improved lifetime and higher catastrophic damage levels.